The subject of my inquiry rendered the method I have described, not only natural but necessary. Yet there are special disadvantages, to which progressive history is not liable, in publishing a book of this sort by installments. Readers of the earlier parts cannot form a just conception of the scope and object of the whole. They cannot perceive the relation of its several sections to each other, or give the author credit for his exercise of judgment in the marshaling and development of topics. They criticise each portion independently, and desire a comprehensiveness in parts which would have been injurious to the total scheme. Furthermore, this kind of book sorely needs an Index, and its plan renders a general Index, such as will be found at the end of the last volume, more valuable than one made separately for each part.